1. Field of the Invention
This invention relates to a time indicator and, in particular, to a time indicator badge which provides a clearer indication of expiration.
2. Prior Art
A preferred prior art time indicator is described in U.S. Pat. No. 4,212,153, of Kydonieus et al. This invention is an improvement thereon. Other relevant patents include U.S. Pat. Nos. 2,337,534, to Barber, 3,078,182, to Crone, Jr., et al., 3,520,124, to Myers, 3,999,946, to Patel, et al., 4,643,122, to Seybold. 4,646,066, to Baughman, et al., and 4,737,463 to Bhattacharjee, et al.
U.S. Pat. No. 4,212,153 to Kydonieus et al, describes a laminated time indicator including a two-layer front indicator part and a two-layer rear reservoir part. The front indicator part has an indicator layer with an outer display surface and an inner surface having an adhesive layer thereon. For example, a pressure- sensitive adhesive coated onto an opaque barrier layer such as vinyl. The rear reservoir part has a dye or ink film layer and a support card layer. When assembled, the front part is placed on the rear part with the ink film layer forming an assembly joint with the adhesive layer. The dye or ink dissolves in the adhesive. After a period of time, the ink migrates from the ink film layer through the adhesive layer and indicator layer to be displayed on the outer surface. In one day, for example, the dye or ink may only reach 20% to 30% of its potential color capacity due to the gradual migration (or adsorption) of the dye into the opaque indicator layer and due to the fact that as the concentration of dye increases at the surface, the process rate decreases. Thus, there is no clear indication of when the indicator expires. It is believed that the reason this prior art device has such deficiencies is due to the fact that the opaque indicator layer must be relatively thick to provide mechanical strength. Such thickness creates a long path through which the dye or ink must migrate, this causing a gradual darkening of the indicator. Further, the opaque indicator layer must have a relatively large quantity of filler, e.g. titanium dioxide, to make it opaque, not just translucent. This filler intermixes and/or adsorbs the dye as the dye migrates through the indicator layer and dilutes or decreases the intensity of the dye. Thus, a red dye or ink will mix and/or be adsorbed with the titanium dioxide and become pink. Applicant's invention overcomes these deficiencies.
U.S. Pat. No. 2,337,534 to Barber, describes a magazine page exposure time indicator including a photosensitive paper sheet mounted on a magazine page, and a developed photographic film sheet having a series of adjacent portions of varying density mounted over the photosensitive paper sheet.
With respect to the other relevant art:
U.S. Pat. No. 3,078,182 to Crone, Jr., describes a heat-sensing, color-changing, adhesive tape for a device to be sterilized in a hospital autoclave including an adhesive layer for attachment, a backing web over the adhesive layer and a visible colored layer over the backing web wherein the colored layer comprises a selective pigment dispersed in a resin binder.
U.S. Pat. No. 3,520,124 to Myers, describes a parked car . time indicator including a first sheet having a first reactant and a second sheet having a second reactant and a release sheet which is peeled away to permit contact of the first sheet with the second sheet to start a reaction over a selective time interval terminating with a color change of the reactants.
U.S. Pat. No. 3,999,946 to Patel, describes a perishable product time-temperature history indicator including a substrate for attachment to the product .showing changes in temperatures along a Y-ordinate over periods of time along an X-ordinate.
U.S. Pat. No. 4,643,122 to Seybold, describes a tamper-indicating security tag including a carrier material impregnated with a solution of a selective compound with a solvent for use in a sealed enveloping container which controls the rate of diffusion of the solvent.
U.S. Pat. No. 4,646,066 to Baughman, describes an environmental exposure indicator device including a target made of a tuned circuit and selective element which receives an interrogation signal in the radio or microwave frequency range and including an antenna which then receives and converts the signal to an electrical current, wherein the selective element has an electrical property that changes in response to an environmental exposure, such as temperature, combined time-temperature, humidity, radiation, a particular fluid, or mechanical shock.
U.S. Pat. No. 4,737,463 to Bhattacharjee, describes a perishable product, photoactivatable time-temperature indicator comprising a mixture of a thermally unreactive diacetylenic compound, and a photosensitive compound that, on exposure to actinic radiation, forms an acid that converts the diacetylene to a thermally reactive product, and an aqueous polymeric medium.